Paula Scotti Campos

Electrolyte leakage and lipid degradation account for cold sensitivity in leaves of Coffea sp. plants

Five Coffea genotypes differing in their sensitivity to low positive temperatures were compared with regard to the effects of chilling on membrane integrity, as well as their ability to recover from cold-induced injury upon re-warming. Membrane damage was evaluated through electrolyte leakage, changes in membrane lipid composition and malondialdehyde (MDA) production in control conditions (25/20 degrees C, day/night), after a gradual temperature decrease period to 15/10 degrees C, after chilling treatment (3 nights at 4 degrees C) and upon re-warming to 25/20 degrees C during 6 days (recovery). C. dewevrei showed the highest electrolyte leakage at 15/10 degrees C and after chilling. This was due mainly to lipid degradation observed at 15/10 degrees C, reflecting strong membrane damage. Furthermore, MDA production after chilling conditions indicated the occurrence of lipid peroxidation. A higher susceptibility of C. dewevrei to cold also was inferred from the complete absence of recovery as regards permeability, contrary to what was observed in the remaining plants. Apoatã and Piatã presented significant leakage values after chilling. However, such effects were reversible under recovery conditions. Exposure to cold (15/10 degrees C and 3 x 15/4 degrees C) did not significantly affect membrane permeability in Catuaí and Icatú. Furthermore, no significant MDA production was observed even after chilling treatments in Apoatã, Piatã, Catuaí and Icatú, suggesting that the four genotypes had the ability to maintain membrane integrity and/or repair membrane damage caused by low temperatures. Apoatã, Piatã and, to a lower extent, Catuaí, were able to cope with gradual temperature decrease through an enhanced lipid biosynthesis. After acclimation, Piatã and Catuaí showed a lowering of digalactosyldiacylglycerol to monogalactosyldiacylglycerol ratio (MGDG/DGDG) as a result of enhanced DGDG synthesis, which represents an increase in membrane stability. The same was observed in Apoatã after chilling, in spite of phospholipids decrease. The studied parameters clearly indicated that chilling induced irreversible membrane damage in C. dewevrei. We also concluded that increased lipid synthesis, lower MGDG/DGDG ratio, and changes in membrane unsaturation occurring during acclimation to low temperatures may be critical factors in maintenance of cellular integrity under chilling.

Nitrogen dependent changes in antioxidant system and in fatty acid composition of chloroplast membranes from Coffea arabica L. plants submitted to high irradiance

Abstract In the present work we investigated the contribution of N availability to the changes in some antioxidant systems and in fatty acid composition of chloroplast membranes, in order to evaluate their role in the high light acclimation in coffee plants. Young coffee ( Coffea arabica L. cv. Catuai) plants, grown under low irradiance (up to 150 μmol m −2 s −1 ) with high (2 N ), medium (1 N ) and low (0 N ) N availability, were exposed to high irradiance (up to 1500 μmol m −2 s −1 ) for a maximal period of 15 days. Changes in several parameters were monitored during that period in the two top pairs of mature leaves. The formation rate of superoxide (O 2 ⋅− ) estimated by ESR ( K f ) did not differ among N -treatments before the onset of high light, but increased 70 and 30% in 0 N and 1 N plants, respectively, and decreased 33% in 2 N plants by the end of the stress. By this time, the chloroplastic activities of Cu,Zn-superoxide dismutase (Cu,Zn-SOD), ascorbate peroxidase (APer) and glutathione reductase (GRed) increased, respectively, 18, 225 and 138% in 2 N plants. The 0 N plants presented a 120% increase in Cu,Zn-SOD activity (which agrees with the higher K f of O 2 ⋅− ) and a 68% decrease in APer activity, suggesting an increase in H 2 O 2 levels, while GRed activity decreased 20%. The total carotenoid content was higher in 2 N plants and increased (about 20%) only in these plants by the end of stress. After 12 days of high irradiance, the total fatty acid (TFA) content increased about 30% in 2 N and 1 N plants, but did not significantly change in 0 N plants. In 2 N and 1 N plants a preferential synthesis of palmitic acid (16:0) and a decrease in the linolenic acid (18:3) percentage caused a decrease in the unsaturation level, which may have made the chloroplast membranes less susceptible to peroxidation. The N dependent changes observed in 2 N (and to a lesser extent in 1 N ) plants could represent adaptive features under the new high irradiance conditions, which increased the protection of the chloroplast structures against photooxidative stress.

High Irradiance Impairments on Photosynthetic Electron Transport, Ribulose-1,5-bisphosphate Carboxylase/ oxygenase and N Assimilation as a Function of N Availability in Coffea arabica L. Plants

Summary Young coffee (Coffea arabica L.) plants grown under low irradiance (PPFD up to ca. 150μmol m−2s−1) and high (2N), medium (IN) and low (ON) nitrogen availability conditions were exposed to natural sunlight (noon PPFD up to ca. 1,700 (¼mol m−2s−1) for 14–15 days, during which parameters related to photosynthesis and nitrogen assimilation were monitored. In the plants with lower N availability, a donor and an acceptor side photoinhibition may have affected PS II functioning. During the high irradiance stress the plants with higher N availability maintained the highest contents of cytochromes (cyt) b559HPJ, b559LP, b563 and f, and in plastoquinone-9 (PQ-9). Those plants also presented significant increases in rubisco content and activity, and a preferential investment in rubisco rather than in light harvesting components by the end of the high irradiance stress. Despite the effects observed on PSII and rubisco, the PS I activity and cyt b6/f complex were much more affected in all N treatments. Leaf nitrate reductase activity decreased whereas nitrate and amino acid contents increased during the high irradiance in 0N and 1N plants. Our data shows that high irradiance affected both the photochemical and enzymatic reactions of photosynthesis (especially in ON and 1N plants), that PS I was a preferential photoinhibitory target and that the higher N availability promoted the recovery of important physiological parameters, such as electron transport rates, PQ-9 and rubisco activity and content.

Effects of an abscisic acid pretreatment on membrane leakage and lipid composition of Vigna unguiculata leaf discs subjected to osmotic stress

Abstract In leaf discs of Vigna unguiculata cv. EPACE-1 subjected to osmotic stress (PEG MW 8000, −1.3 MPa) a significant decrease in membrane integrity occurred, as evaluated by electrolyte efflux. This effect was significantly reduced when discs were treated with ABA (0.1 mM in Tris buffer) prior to PEG treatment. In PEG-treated discs, membrane lipids were drastically degraded, particularly the galactolipids. The percentage of linolenic acid in MGDG also decreased significantly. An ABA pretreatment of discs before osmotic stress significantly decreased galactolipid degradation and preserved their linolenic acid content. We concluded that ABA had a protective effect on membranes against osmotic stress, as attested by electrolyte leakage test and polar lipid analysis. Some possible roles for exogenous ABA in the acquisition of such an enhanced capacity to maintain membrane integrity under dehydration conditions are suggested.

Biofortification of durum wheat (Triticum turgidum L. ssp. durum (Desf.) Husnot) grains with nutrients

ABSTRACT Durum wheat (Triticum turgidum L. ssp. durum (Desf.) Husnot) was grown under conditions to promote mineral biofortification at the grain level. Along plant development, biomass accumulation and the kinetics of nutrients accumulation were assessed, identifying the nutrient fluxes of roots and shoots, and the timescale constraints of crop biofortification. Plants were grown under environmentally controlled conditions, submitted to four increasing concentrations of nutrient solutions (1-, 2-, 4- and 6-fold) of micro- (Fe, Zn, Cu and Mn) and macronutrients (Ca, K, P and Mg). The threshold of mineral toxicity was not reached as evaluated through plant biomass accumulation, but considering grain yield, the twofold nutrient concentration was the best treatment for biofortification. In the different treatments, the contents and the mineral unrests of roots uptake and shoots translocation varied, at different magnitudes and trends, before the onset of booting and from the physiological maturity onwards. Except for Cu, all mineral nutrients were mainly detected in the bran and embryo of the grains; therefore, the production of biofortified pasta for human consumption requires the use of integral semolina.